PROJECT SUMMARY Coronary artery disease (CAD) remains among the highest disease burdens in the modern world. Despite effective treatments focused on specific risk factors such as LDL cholesterol (LDL-C), prevalence and mortality from this disease remains very high. This necessitates investigating additional risk factors and identifying novel targets for treatment. Apolipoproteins C-III and A-V are reciprocal regulators of TG in plasma and were recently implicated through human genetics as being significantly related to risk of developing CAD. Genetic studies suggested that inactivating ApoC-III or enhancing ApoA-V, may protect against CAD. However, we currently have very little understanding of the structure and mechanisms of these two proteins and how the disease-associated mutations exert their effects to regulate TG levels and CAD risk. In this proposal, we seek to elucidate the helical and structural dynamics of the wild-type (WT) forms of these two apolipoproteins in the lipid-free and lipid-bound states through hydrogen-deuterium exchange and mass spectrometry to amino acid- level resolution. We will also study the effects the identified coding mutations on protein folding, dynamics, and lipid binding. We posit that the identified mutations influence lipid binding and cause altered TG metabolism through impacting lipoprotein association, LPL activity, TG-rich lipoprotein clearance and hepatic TG metabolism. We will test hypotheses for how each variant is acting through biochemical approaches and complementary in vivo studies comparing expression of WT and mutant ApoC-III/A-V in humanized mouse models. Finally, we will assess the impact of the CAD-associated ApoC-III/A-V mutations on atherogenesis in vivo. The proposed experiments will decipher the specific mechanisms of action of ApoC-III and ApoA-V in regulating TG metabolism and risk of CAD, and determine the structural features most crucial to these functions.